Practice PnG Driving Profile


Normalizing Practice Cycles



Mileage Results


For a 9 MPG fuel savings, we have to vary the vehicle speed by 18 mph, which impacts the driving of any following vehicle and driver.

Driving Profiles



Energy Per Meter, 15-25 mph

The Graham miniscanner has the ability to record the engine shaft power as well as the traction battery charge and discharge. Since these are the only sources of motive energy, it provides the fine resolution needed to measure the vehicle energy demands when dealing with MPG values beyond the vehicle 99.9 indicator:

Measuring the engine and battery energy avoids trying to calculate subtle engine thermodynamic effects (aka., BSFC and cycle times) over the very long intervals needed to draw reasonable conclusions. This result is more consistent with the expected value from pulse and glide.

Analysis

Inertial energy is a conservative function. This means that in the absence of drag, potential and kinetic energy transfer with nearly 100% efficiency ... this is how planets and moons remain in orbit for billions of years.

Rolling drag can be treated as a constant for ordinary speeds above 0 mph. There are some non-linear effects associated with transaxle lubricant stiring and tire deformations at high speeds, 80 mph, but these are minor at these speeds. If rolling drag is the only effect, the energy needed would vary with the vehicle speed so slow or fast wouldn't matter.

Aerodynamic drag is the primary source of energy loss and varies by the square of the velocity. As pointed out in the Lee, Nelson and Lohse-Busch report "Vehicle Inertia Impact on Fuel Consumption of Conventional and Hybrid Electric Vehicles Using Acceleration and Coast Driving Strategy" (SAE 2009-01-1322):

Depending upon the average speed of any given pulse and glide protocol, a significant portion will be spent at speeds above the equivalent steady-speed in a V**2 drag region. The rest of the time will be spent under the V**2 region. We can evaulate how much energy is lost by integrating the drag forces above and below the equivalent, steady state speed over the distance of a single cycle. Force times distance is the energy required to sustain the object in either protocol (insert integration formula here. RJW)

The Lee, Nelson and Loshe-Busch paper suggests that the acceleration should be proportional to the vehicle speed that the optimum acceleration profile should increase as vehicle speed. However, engine BSFC has not been included in this study to fully model vehicle performance (or perhaps not fully explained.)

We know typical Otto engines don't reach peak BSFC until their throttle is full open and even then varies in a non-linear fashion with engine rpm. In contrast, the Prius BSFC is nearly linear over a wider range. Any optimum Pules and Glide model needs to include these factors.

Safety and Effectiveness in Traffic

I agree that Pulse and Glide needs to be limited to closed tracks or very low traffic roads. The speed differences required for pulse and glide means as the number of vehicles increase, the probability of having to brake to maintain vehicle safety distances increases. This reduces the effectiveness of Pulse and Glide and worse, reduces road capacity to sustain traffic. It is a technique best practiced solo.

Even with cooperation, as the number of vehicles increase, the 'tail end Charlie' driver will be reacting to the lead vehicles versus a disciplined Pulse and Glide. The lead driver has a great ride but the following vehicles and drivers are subject to less than optimum performance. Pulse and glide does not scale well with as traffic density increases.